1. Field of the Invention
The present invention corresponds to a method and device for quantitative evaluation of status of bones implying assessment of bone mechanical properties, mineralization (ossification), porosity and fracture risk, and detection of local lesions.
2. Description of Related Art
The importance of assessment of bone quality is mainly related to the necessity for diagnostics of osteoporosis. Osteoporosis presents a common public health problem becoming increasingly important as population ages, affecting a large proportion of post-menopausal women and senile people of both genders. Secondary osteoporosis and complicated osteopenia are factors inherent to a variety of metabolic and endocrine disorders that require monitoring during treatment of the primary disease. Monitoring of skeletal growth and maturation is a measure to assess in general healthy development of children and adolescents by right nutrition and sufficient exercise that is of critical importance in the formation of strong musculoskeletal systems and in preventing osteoporosis later in life. The pediatric application strongly demands accounting the growth process.
Conventional means of bone quality diagnostics include radiography and planar X-ray which are usually applied in orthopedics for visualization of bone lesions, deformities, displacements, etc. Roentgenography is traditionally applied to determine the degree of ossification and synostosis for assessment of skeletal age and clearly shows clinical manifestations of osteoporosis like vertebral compressions at the developed stage. Although relatively insensitive for detection of osteopenia and examination of mineral content, the conventional radiography detects bone loss only when it achieves 30-40%.
Widely applied for assessment of postmenopausal and senile osteoporosis, radiological densitometers include families of whole body and peripheral scanners, utilizing single- and dual-energy photon apsorptiometry (SPA, DPA), dual-energy x-ray absorption (DXA), and peripheral quantitative computed tomography (pQCT). The main advantage of these instruments is their ability to measure bone mass, bone mineral content and bone mineral density with high precision and to access the most responsive sites such as the spine and hip. The pQCT provides measurements of both the cross-section size and density of the bone without influence from the overall body size that is particularly important for the evaluation of bone resorption during osteoporosis and accumulation of bone mass in growing bones of children. Unfortunately, there are multiple reasons, which include high cost, lack of portability and hazardous radiation exposure, that limit availability of this technique encumbering its use in wider screening and monitoring of the at-risk population. In addition, volumetric measurements of bone substance by radiation absorption do not reveal changes in mechanical and micro-structural properties associated with bone toughness and brittleness that are other factors of bone fracture risk.
Quantitative ultrasound (QUS) presents an alternative to the x-ray densitometry, based on measurement of parameters of propagation of elastic waves through bone and interaction of the waves with bone substance. The ultrasound parameters, including velocity of ultrasound and frequency slope of attenuation, relate to elastic mechanical properties and structure of in vivo bone. The ultrasonometers present several advantages, such as: (1) provision of information on the elastic properties and structural changes (porosity) of bone, which is not accessible by DXA; (2) no irradiation hazard, allowing radiation-safe and off-repeated measurements; (3) portability, ease of use, and lower costs. The QUS devices are highly specialized in relation to application and are classified as sonometers for heel, phalanx, tibia and multi-site testing devices.
Conventional solutions have included proposing different modifications of ultrasound bone analyzers, applying pulse transition methods to heel bone and varied approaches for transducers application and signal processing. For example, U.S. Pat. No. 4,774,959 describes a narrow band ultrasonic frequency attenuation bone measuring system. U.S. Pat. No. 5,349,959 describes an ultrasonic densitometer device and method. U.S. Pat. No. 5,720,290 relates to an apparatus and method for acoustic analysis of bone using optimized functions of spectral and temporal signal components. Introduction of a number of transducer locations and bone imaging through the scanning procedure allowed to increase precision of diagnostics by direct detection of xe2x80x9cregion of interestxe2x80x9d, being important due to bone spatial heterogeneity, as described in U.S. Pat. No. 5,840,029 of an imaging ultrasonic densitometer and U.S. Pat. No. 6,086,538 of a method and apparatus for evaluation of bone condition. Other recent attempts to increase reliability of diagnostics were aimed to create a united systems incorporating an ultrasonometer and biomarkers, as described in U.S. Pat. No. 6,029,078 as a system for assessing bone characteristics, and to increase accuracy by multiple contact applications, as described in U.S. Pat. No. 6,135,964 as an ultrasonic bone testing apparatus with repeatable positioning and repeatable coupling. The conventional QUS techniques for long bones utilize a relatively simplified recording of ultrasound velocity at cross-bone or along-bone propagation influenced by both bone geometrical and material properties and present no information about their separate contribution. The following limitations of conventional QUS are found.
1) There is a numerical superiority of heel QUS techniques over long bone QUS, allowing good opportunity to evaluate density of trabecular structure in osteoporosis, but limiting QUS application for other sites of the skeleton, thereby hampering comprehensive evaluation of osteoporosis and monitoring of bone growth and ossification during childhood;
2) Existing long bones QUS obtain non-specified integral data on changes of bone geometrical (cortical thickness), material (stiffness, mineralization) and structural (porosity) properties.
3) The conventional QUS devices for long bones do not provide a scanning option, capable of presenting spatial characteristics of bone growth, ossification and atrophy.
The present invention relates to a method of assessment of bone condition in which a probe takes unilateral sequential ultrasonic measurements along a trajectory of the bone. The probe includes emitting and receiving transducers. Ultrasound propagation parameters can be calculated from ultrasonic signals received at the receiving transducer and distance readings acquired along the trajectory. The set of measured and displayed ultrasonic parameters can include: velocity of a longitudinal wave; velocity of a flexural wave; attenuation of the longitudinal wave; attenuation of the flexural wave; frequency slope of attenuation of the longitudinal wave; frequency slope of attenuation of the flexural wave; changes of spectral characteristics of propagating the longitudinal wave; and changes of spectral characteristics of propagating the flexural wave. The ultrasound propagation parameters can be evaluated for determining characteristics of the bone.
The present invention for the method and device for multi-parametric ultrasonic assessment of bone conditions has the advantages of: 1) the ability to scan examined trajectory along bone and to present spatial distribution of ultrasonic parameters; and, 2) to examine bone by different ultrasonic wave modes (longitudinal and flexural) and on variable ultrasonic frequencies and to extract comprehensive parameters illustrative on the elastic, geometrical and structural properties of bone. Clinical benefits provided by the present invention are listed below.
1. Measurements of velocity of a flexural wave provide an opportunity to determine cortical thickness of bone. The cortical thickness of bone can be used to estimate the degree of resorption during osteoporosis, usually progressing from the bone channel, as well as to evaluate the accumulation of bone mass in children and adolescents during skeletal growth.
2. Measurements of velocity of a longitudinal wave can be used to evaluate the elastic properties of the bone matrix sensitive to accumulation of micro-defects during osteoporosis and to the level of osteoid mineralization during bone development.
3. The combined stiffness index from the flexural and longitudinal velocities provides information about the total mechanical endurance of bone and its capacity to withstand loading.
4. The frequency slope of attenuation combined with derivatives of signal spectrum form a bone structural index, sensitive to changes of porosity and size of structural components, presence of voids and spatial defects.
5. Longitudinal profiles of ultrasonic parameters provide valuable information on spatial distribution of bone characteristics. This permits the estimation of the stage of atrophy expansion along the bone that usually initiates in the epiphyseal and metaphyseal area of long bones during osteoporosis, continuously involving a larger area toward the diaphysis. As for the pediatric application, the longitudinal profiles can be used to monitor bone growth area and to determine bone ossification status, as well as skeletal age by cessation of growth zones.
6. Detection of local weakness areas like cysts or poorly consolidated fractures and determination of spatial length of the areas can be carried out through analysis of the longitudinal profiles.
7. The exclusion of soft tissues influence by introducing an auxiliary pulse-echo mode provides increased accuracy of measurements and makes possible examination of skeletal areas under thicker soft tissue layers.
8. The automatic determination of a xe2x80x9cregion of interestxe2x80x9d by processing of the longitudinal profiles provides a reliable reference to anatomical landmarks of bone in order to obtain comparable data.
The invention will be more fully described by reference to the following drawings.